Microphones can be exposed to environments where sound levels, described on a log scale using units of decibels of sound pressure level (dB SPL), can range from very quiet (e.g., less than 25 dB SPL) to very loud (e.g., 140 dB SPL). In addition, microphones are typically required to maintain their performance over a large signal range, e.g., up to 120 dB. Simultaneously, microphones are required to exhibit very small intrinsic noise in order to make weak audio signals detectable, while they also need to handle very large audio signals without significant distortion. As a result, such requirements dictate that microphones have a very large dynamic range (DR).
Analog and digital microphones output a voltage or digital output stream, respectively, corresponding to the audio signal sensed by the microphone. The advantage of a digital microphone is that its digital output stream is relatively immune to noise and that an analog-to-digital converter (ADC) is not required to perform digital signal processing on the microphone digital output stream. However, one disadvantage of a digital microphone is that its dynamic range is often lower than what can be achieved with an analog microphone due to constraints in the power consumption that can be allocated to the microphone within many applications.
Conventional solutions for improving DR of a digital microphone can include techniques such as employing one or more of a high DR ADC or employing an automatic gain control amplifier (AGC) which can significantly lower ADC DR requirements while still meeting the desired max SPL and noise floor levels of the overall digital microphone. However, such conventional solutions can require excessively large power consumption and/or introduce troublesome artifacts. Other solutions can require specific analog front ends that are likely to suffer from low signal to noise ratio (SNR) performance or multipath approaches that, due to the combining algorithm can suffer from instantaneous saturation effects. In addition, the ability to integrate a high DR digital microphone is desirable for implementation in devices such as mobile devices that can be exposed to a variety of widely varying SPL environments. For example, a digital microphone comprising one or more microelectromechanical systems (MEMS) acoustic sensors with a component implementing an algorithm for high DR in complementary metal oxide semiconductor (CMOS) processes can provide a low power, high DR digital microphone suitable for such mobile devices.
It is thus desired to provide high dynamic range digital microphones that improve upon these and other deficiencies. The above-described deficiencies are merely intended to provide an overview of some of the problems of conventional implementations, and are not intended to be exhaustive. Other problems with conventional implementations and techniques, and corresponding benefits of the various aspects described herein, may become further apparent upon review of the following description.